1. Field of Invention
The techniques described herein relate generally to conversion of electrical power produced by a generator into AC power suitable for distribution or other uses. Such techniques may be used to convert electrical power produced by a wind turbine generator into AC power that may be provided to an electrical grid, for example.
2. Discussion of the Related Art
The modern industrial world requires large amounts of electrical power each and every day. To produce electrical power, electrical generators are designed and manufactured to convert energy from another form into electrical energy. Renewable energy sources to drive electrical generators are of interest and there is a class of generators that produce electrical energy by converting mechanical energy (e.g., from a natural or renewable source) into electrical energy. For example, wind turbine generators are designed to generate electrical power in response to mechanical rotation of turbine blades that capture wind energy and that are mechanically coupled to a rotating shaft that drives a rotor of an electrical generator to produce electrical power.
Various types of generators exist that are designed to convert mechanical rotation into electrical power through a magnetic coupling that produces current in response to a changing magnetic field. Examples of such generators include synchronous generators and induction generators. One example of a synchronous generator is a permanent magnet generator. A permanent magnet generator produces a changing magnetic field using permanent magnets on the rotor. Another example of a synchronous generator is a field-excited generator. A field-excited generator produces a changing magnetic field using an electrical current established through a conductor on the rotor. In a synchronous generator, a changing magnetic field produced by the rotor causes a conductor on the stator to produce electrical current. In an induction generator (e.g., a doubly fed induction generator or DFIG), eddy currents are induced in the rotor using a magnetic field, and the rotation of the rotor produces a rotating magnetic field that induces current in the stator winding. Synchronous and induction generators used in wind turbine generators generally produce alternating current (AC) voltages and currents (i.e., AC power).
The power produced by a wind turbine generator may be provided to an electrical power grid or stored. An electrical power grid (hereafter also referred to as a “grid”) typically provides AC power to consumers such as a plant and/or multiple consumers in a region or geographic location. The grid may receive power from one or multiple wind turbines and/or other sources (e.g., coal powered generators) and distribute the power to end-consumers that may be relatively local or may be distributed over a relatively large geographic area or region. As such, the grid may be required to operate in accordance with generally tight specifications with respect to acceptable levels of voltage and frequency (among other specifications), and are often regulated by grid codes established for a particular region. The AC power produced by a wind turbine generator typically cannot be provided directly to the grid, as the voltages produced by a wind turbine generator itself are generally variable in magnitude and frequency and without modification therefore would not likely meet the specifications of the electrical power grid to which it is intended to provide electrical power.
To address this issue, power electronics are typically used to convert the AC power produced by a wind turbine generator into AC power suitable for and expected by the electrical power grid. In a typical design, the power electronics include an alternating current to direct current (AC/DC) conversion module to convert the AC power from the wind turbine into a direct current (DC) voltage, and a direct current to alternating current (DC/AC) conversion module to convert the DC power into AC power suitable for the grid to which the wind turbine is to provide power. Such power electronics may be implemented as a power converter within or as part of a wind turbine and may be coupled to the wind turbine generator at its input and configured to couple to the grid at its output (e.g., through an output pad and/or transformer).